Hirsutella thompsoniU a fungal pathogen of mites. II. Host‐pathogen interactions

SUMMARYThe moniliaceous fungus, Hirsutella thompsoniU grown on potato‐dextrose agar (PDA) or on sterile wheat bran, was highly pathogenic to the carmine spider mite, Tetranychus cinnabarinus, and, grown on PDA, to the oriental spider mite, Eutetranychus orientalis. The fungus penetrated the mites' integument mainly through the legs and formed hyphal bodies in chains in the haemolymph. Hyphae, on which the spores were produced, began to emerge through the genital and anal apertures and then all over the body. Various mycophagous mites, a predaceous species and the tick Argas persicus were immune. H. thompsonii grew well on cadavers of diverse insects and mites.The fungus killed most mites and quickest, usually by the 2nd day, at 25o, 27o and 30 oC; least at 13o and 35 oC. It sporulated best on mites at 24o, 27o and 30 oC (full sporulation at 27 oC took place within 12 h after death); it was good, but slower, at 13o and 35 oC. The fungus germinated, penetrated mites and sporulated there very poorly below 100% r.h. When the daily number of hours at 100% r.h. was reduced from 24 to 18 or 6 h, fungus‐associated mortality dropped greatly.In the field, use of the fungus for mite control would be suitable particularly in tropical and humid subtropical areas, and its success in Israel would not be assured. In glasshouses, H. thompsonii could induce epizootics in Israel and elsewhere only if humidities were raised to saturation and the daytime temperature kept below 37 oC.